The subject matter disclosed herein relates to an apparatus for attaching a device to the outer surface of a circular structure, and more particularly, to an apparatus for coupling a nondestructive testing device to the outer surface of a pipe.
Several industries (e.g., oil and gas, refinery, chemical, power generation) require the transport of fluid (e.g., liquids or gases) through pipes. Nondestructive testing devices can be placed on the outer surface of these pipes to monitor corrosion/erosion of the pipes, including corrosion/erosion on the interior of pipe walls. In many cases, the probe or other nondestructive testing device is permanently coupled to the outer surface of the pipe at a single location to continuously monitor corrosion/erosion at that location to determine pipe corrosion/erosion rates and to determine whether that pipe location is in need of preventative maintenance to prevent a pipe failure.
One example of a nondestructive testing device used to monitor corrosion/erosion of a pipe is an ultrasonic testing device. When conducting ultrasonic testing of a pipe, an ultrasonic pulse is emitted from a probe coupled to the outer surface of the pipe and passed through the pipe wall. As the ultrasonic pulse passes into and through the pipe wall, various pulse reflections called echoes are reflected back to the probe as the pulse interacts with the outer surface of the pipe, internal structures within the pipe wall, and with the back wall of the pipe wall. The echo signals can be displayed on a screen with echo amplitudes appearing as vertical traces and time of flight or distance as horizontal traces. By tracking the time difference between the transmission of the ultrasonic pulse and the receipt of the echoes, various characteristics of the pipe can be determined, including pipe wall thickness. If the thickness of the pipe wall at the location of the ultrasonic testing device decreases over time (e.g., as would be shown be a reduction in the time of flight of the back wall echo), this can be an indication of corrosion/erosion.
Since much of the analysis in ultrasonic testing, as well as other nondestructive testing techniques (e.g., electromagnetic, infrared/thermal, radiographic, etc.), is based on comparisons of current measurements to past measurements or to known measurements based on calibration or original dimensions, it is necessary to ensure that the position and coupling of the probe in relation to the outer surface of the pipe remain fixed and unchanged over time. For example, if the probe remains coupled to the outer surface of the pipe but moves along the outer surface of the pipe from one location to another, this can lead to inaccurate results based on the comparison of data from two different locations on the outer surface of the pipe. Similarly, if the probe becomes decoupled from the outer surface of the pipe or the coupling force between the probe and the outer surface of the pipe changes, this can result to inaccurate results based on the comparison of data from different coupling positions on the outer surface of the pipe or different coupling forces. For instance, if the probe was not properly coupled to the outer surface of the pipe, this could lead to inaccurate time of flight data that would fail to accurately indicate the amount of corrosion/erosion at a location of the pipe. In some cases, the decoupling could be so significant that it would prevent the ability of the probe to transmit the ultrasonic pulse through the pipe wall to conduct any testing.
One existing solution for coupling a probe or other nondestructive testing device to the outer surface of a pipe is a metal clamp that includes a U-bolt fastened to a clamp body, wherein the bend of the U-bolt is fitted around one side (e.g., the bottom) of the outer surface of the pipe and the threaded ends of the U-bolt are fastened to the clamp body that extends from one threaded end of the U-bolt to the other across the opposite side (e.g., the top) of the outer surface of the pipe. In some installations where a probe is required on opposite sides of the pipe, rather than use a U-bolt, conventional bolts can attach one clamp body on one side of the pipe to another clamp body on the opposite side of the pipe. Since the clamp bodies, U-bolts, and/or bolts used in this existing metal clamp are sized based on the outer diameter of the outer surface of the pipe (e.g., in the range of 2″ (50.8 mm) to 40″ (1,016 mm)), a single metal clamp design can typically only be used for two or three different sized pipes (e.g., one metal clamp can only be used for 6″ (152.4 mm), 8″ (203.2 mm), and 10″ (254 mm) pipes). Also, given the configuration of the existing metal clamp, a single metal clamp design can typically only be used to accommodate one or two probes on the circumference of the outer surface of the pipe at a particular location (e.g., on the top and bottom of the pipe, but not on the sides, or on the left side and right side of the pipe, but not on the top and bottom).
In the existing bolt or U-bolt metal clamp, the portion of the clamp body contacting the outer surface of the pipe can include an opening into which the probe can be installed. In some installations, a metal block is placed over the cavity after the probe is installed in the cavity. One or more bolts can then be tightened to apply force down onto the probe until the desired coupling force between the probe and the outer surface of the pipe is achieved. While this existing bolt or U-bolt metal clamp is capable in some cases of ensuring that the position and coupling of the probe in relation to the outer surface of the pipe remain fixed and unchanged over time, there can be circumstances where this is not the case. For example, the use of multiple bolts on the clamp body to establish the desired coupling force introduces the possibility that, if one bolt is tightened more than another, certain parts of the probe may be coupled to the outer surface of the pipe at different coupling forces than other parts of the probe.
Changes in temperature of the existing clamp and the pipe over time can also result in changes in the position and coupling of the probe in relation to the pipe by changing the shape of the metal clamp and the pipe. For example, if the fluid being transported through the pipe is at a high temperature (e.g., greater than 350° C.), the pipe can be heated to this high temperature, resulting in thermal expansion of the pipe (i.e., increase in the outer diameter of the pipe), which may bend or otherwise deform the clamp body or U-bolts/bots of the existing metal clamp. In addition, if the pipe is heated to this high temperature, the existing metal clamp, which is in contact with the outer surface of the pipe, can also be heated to this high temperature, making the existing metal clamp more malleable and likely to bend or otherwise deform. To the extent that the pipe and existing metal clamp are made of different materials (e.g., stainless steel, carbon steel), the effect of the high temperature on the pipe and existing metal clamp may differ (e.g., different amounts and rates of thermal expansion and contraction). Even if the pipe and existing metal clamp are made of the same material, the effect of the high temperature on the pipe and existing metal clamp may differ based on the different ambient conditions of the pipe and the existing metal clamp. The continuous temperature cycling (e.g., thermal expansion and contraction) of the pipe and the existing metal clamp can result in changes in the position and coupling of the probe in relation to the pipe. In some cases, the temperature cycling may be so significant over time that the probe becomes decoupled from the outer surface of the pipe, requiring that the existing metal clamp be removed and replaced in a laborious process. In order to minimize temperature cycling, the size and thickness of the existing metal clamp can be significantly increased, which increases the difficulty of handling and installing the clamp and undesirably increases the weight of the clamp on the pipe.
It would be advantageous to provide an apparatus for attaching a device to the outer surface of a pipe that does not have the disadvantages associated with the existing metal clamp.